I've been running Subscriber successfully for several months. Recently I moved my whole website to a new domain and now the Subscriber script doesn't work. All the paths are identical. What has changed? Is vars.txt effected?

If you've change domains you're going to have to change the URLs in the vars.txt to the new domain. Otherwise, you're not going to be able to use the administration scripts and the URLs mailed out the people will be wrong.